In the field of mobile communication systems (for example, Personal Handyphone System: PHS) evolving rapidly these few years, a PDMA (Path Division Multiple Access) system that allows radio mobile terminal devices (hereinafter, terminal) of a plurality of users to effect spatial multiple access to a radio base system (hereinafter, base station) by dividing the same time slot of the same frequency spatially has been proposed in order to improve the usage efficiency of radio frequency.
In this PDMA system, the adaptive array technique is employed. Adaptive array processing is directed to extract a signal properly from a desired terminal by calculating a weight vector composed of reception coefficients (weight) for respective antennas of the base station for adaptive control, based on a reception signal from a terminal.
By such adaptive array processing, the uplink signal from the antenna of each user terminal is received by the array antenna of the base station, and then separated and extracted with reception directivity by the reception weights of the current user terminal.
Since there is no variation in the propagation path (the zone between the antenna end of the base station and the antenna end of the terminal) assuming that the time difference between reception and transmission at the base station is 0, the downlink signal from the base station to the relevant terminal is transmitted from the array antenna of the base station with transmission directivity towards the antenna of the relevant terminal by applying the reception weights obtained at the time of receptions as transmission weight information.
The adaptive array processing set forth above is well known in the field of art, and described in detail in, for example, “Adaptive Signal Processing by Array Antenna” (Kagaku Gijutsu Shuppan), issued Nov. 25, 1998, pp. 35–49, “Chapter 3: MMSE Adaptive Array” by Nobuyoshi Kikuma. The operating mechanism thereof will be described briefly hereinafter.
In the following description, the base station that provides downlink transmission directivity control with respect to a terminal employing such adaptive array processing will be referred to as adaptive array base station hereinafter.
In the PDMA set forth above, the signal of each user is separated using a frequency filter, time synchronization between the base station and each user mobile terminal device, and a mutual interference canceller such as an adaptive array.
FIG. 8 is a schematic block diagram showing a configuration of a transmission and reception system 2000 of a conventional base station for PDMA, realized using an adaptive array radio device.
In the configuration shown in FIG. 8, four antennas #1–#4 are provided to establish identification between a user PS1 and a user PS2.
In a reception operation, the outputs of antennas are provided to an RF circuit 2101 to be amplified by reception amplifiers, and then frequency-converted by a local oscillation signal. The converted signals have the unnecessary frequency signal removed by filters, are subjected to A/D conversion, and then applied to a digital signal processor 2102 as digital signals.
Digital signal processor 2102 includes a channel allocation reference calculator 2103, a channel allocating apparatus 2104, and an adaptive array 2100. Channel allocation reference calculator 2103 calculates in advance whether the signals from two users can be separated by the adaptive array. Based on the calculation result, channel allocating apparatus 2104 provides channel allocation information including user information, selecting frequency and time, to adaptive array 2100. Adaptive array 2100 applies a weighting operation in real time on the signals from the four antennas #1–#4 based on the channel allocation information to separate only the signals of a particular user.
[Configuration of Adaptive Array Antenna]
FIG. 9 is a block diagram showing a configuration of a transmission and reception unit 2100a corresponding to one user in adaptive array 2100. The example of FIG. 9 has n input ports 2020-1 to 2020-n to extract the signal of the desired user from input signals including the signals of a plurality of users.
The signals input to respective input ports 2020-1 to 2020-n are applied via respective switch circuits 2010-1 to 2010-n to a weight vector control unit 2011 and respective multipliers 2012-1 to 2012-n.
Weight vector control unit 2011 calculates weight vectors w1i–wni using input signals, a unique word signal corresponding to the signal of a particular user stored in advance in memory 2014, and the output of an adder 2013. As used herein, subscript “i” implies that the weight vector is employed for transmission/reception with the i-th user.
Multipliers 2012-1 to 2012-n multiply the input signals from input ports 2020-1 to 2020-n by weight vectors w1i–wni, respectively. The multiplied result is applied to adder 2013. Adder 2013 adds the output signals from multipliers 2012-1 to 2012-n to output the added signals as a reception signal SRX(t). This reception signal SRX(t) is also applied to weight vector control unit 2011.
Transmission and reception unit 2100a further includes multipliers 2015-1 to 2015-n receiving an output signal STX(t) to be transmitted from the adaptive array radio base station to multiply the same by respective weight vectors w1i–wni applied from weight vector control unit 2011 for output. The outputs of multipliers 2015-1 to 2015-n are applied to switch circuits 2010-1 to 2010-n , respectively. Specifically, switch circuits 2010-1 to 2010-n provide the signals applied from input ports 2020-1 to 2020-n to a signal receiver unit 1R in a signal receiving mode, and provides the signal from a signal transmitter unit 1T to input/output ports 2020-1 to 2020-n in a signal transmission mode.
[Operating Mechanism of Adaptive Array]
The operating mechanism of transmission and reception unit 2100a of FIG. 9 will be described briefly here.
For the sake of simplfying the description hereinafter, it is assumed that there are four antenna elements, and two users PS effect communication at the same time. In such a case, signals applied to reception unit 1R from respective antennas are represented by the equations set forth below.RX1(t)=h11Srx1(t)+h12Srx2(t)+n1(t)  (1)RX2(t)=h21Srx1(t)+h22Srx2(t)+n2(t)  (2)RX3(t)=h31Srx1(t)+h32Srx2(t)+n3(t)  (3)RX4(t)=h41Srx1(t)+h42Srx2(t)+n4(t)  (4)
Signal RXj(t) represents a reception signal of the j-th (j=1, 2, 3, 4) antenna. Signal Srxi(t) represents a signal transmitted by the i-th (i=1, 2) user.
Coefficient hji represents the complex coefficient of a signal from the i-th user received at the j-th antenna, and nj(t) represents the noise included in the j-th reception signal.
The above equations (1)–(4) may be represented in vector form as follows:X(t)=H1Srx1(t)+H2Srx2(t)+N(t)  (5)X(t)=[RX1(t), RX2(t), . . . RX4(t)]T  (6)Hi=[h1i, h2i, . . . , h4i]T, (i=1, 2)  (7)N(t)=[n1(t), n2(t), . . . n4(t)]T  (8)
In equations (6)–(8), [ ] T denotes the transposition of [. . . ]. Here, X (t) represents the input signal vector, Hi the reception signal coefficient vector of the i-th user, and N (t) a noise vector.
The adaptive array antenna outputs as a reception signal SRX(t) a synthesized signal obtained by multiplying the input signals from respective antennas by respective weight coefficients w1i–wni, as shown in FIG. 9.
Given these preliminaries, the operation of an adaptive array in the case of extracting a signal Srx1(t) transmitted by, for example, the first user is set forth below.
Output signal y1 (t) of adaptive array 2100 can be represented by the following equations by multiplying input signal vector X(t) by weight vector W1.y1(t)=X(t)W1T  (9)W1=[W11, W21, W31, W41]T  (10)In other words, weight vector W1 is a vector with the weight coefficients wj1 (j=1, 2, 3, 4) to be multiplied by the j-th input signals RXj (t) as elements.
Substituting input signal vector X (t) represented by equation (5) into y1(t) represented by equation (9) yields:y1(t)=H1W1TSrx1(t)+H2W1TSrx2(t)+N(t)W1T  (11)
By a well known method, weight vector W1 is sequentially controlled by weight vector control unit 2011 so as to satisfy the following simultaneous equations when adaptive array 2100 operates in an ideal situation. As used herein, the adaptive array processing to obtain such weight vectors determines the optimum weight by minimizing the difference (error signal) between the reference signal that is the desired array response and the actual array output signal. In this minimization of the error signal, the minimum mean square error (MMSE) method is employed.H1W1T=1  (12)H2W1T=0  (13)
If weight vector W1 is perfectly controlled so as to satisfy equations (12) and (13), output signal y1(t) from adaptive array 2100 is eventually represented by the following equations.y1(t)=Srx1(t)+N1(t)  (14)N1(t)=n1(t)w11+n2(t)W21+n3(t)W31+n4(t)W41  (15)
Specifically, signal Srx1(t) emitted from the first of the two users will be obtained for output signal y1(t).
In FIG. 9, input signal STX(t) for adaptive array 2100 is applied to transmitter unit 1T in adaptive array 2100 to be applied to respective one inputs of multipliers 2015-1, 2015-2, 2015-3, . . . , 2015-n. To the other inputs of these multipliers, weight vectors w1i, w2i, w3i, . . . , wni calculated by weight vector control unit 2011 based on reception signals described above are copied and applied.
The input signals weighted by these multipliers are delivered to corresponding antennas #1, #2, #3, . . . , #n via corresponding switches 2010-1, 2010-2, 2010-3, 2010-n for transmission.
Identification of users PS1 and PS2 is made as set forth below. A radio wave signal of a cellular phone is transmitted in frame form. The radio wave signal of a cellular phone is mainly composed of a preamble formed of a signal series known to a radio base station, and data (voice and the like) formed of a signal series unknown to the radio base station.
The preamble signal series includes a signal stream of information to identify whether the current user is the appropriate user to converse for the radio base station. Weight vector control unit 2011 of adaptive array radio base station 1 compares the unique word signal corresponding to user A output from memory 2014 with the received signal series to conduct weight vector control (determine weight coefficients) so as to extract the signal expected to include the signal series corresponding to user PS1.
[Calibration of Adaptive Array Radio Device]
However, even if there is no variation in the propagation path, difference in transmission characteristics such as in the phase rotation and amplitude variation between transmission and reception signals will occur between the reception signal path and the transmission signal path due to the physical difference between the reception signal path and the transmission signal path in the adaptive array base station (for example, due to the difference in the path length, difference in the properties of the device such as amplifiers and filters included in the reception circuit and the transmission circuit, and the like).
If there is difference in the transmission characteristics between the transmission and reception signals within the adaptive array base station, the optimum transmission directivity cannot be directed to the terminal of the transmission destination based on the method that directly employs the reception weight set forth above as the transmission weight.
Thus, calibration is generally carried out to compensate for the difference between the transmission characteristic of the reception signal path and the transmission characteristic of the transmission signal path within the base station at the time of shipment from the factory to achieve the optimum transmission directivity.
FIG. 10 is a schematic block diagram to describe the configuration of a calibration system 3000 directed to conducting, at the time of shipment from the factory, calibration with respect to adaptive array base station 3010 identified as the base station.
Referring to FIG. 10, calibration-system 3000 includes an adaptive array radio device 3010 that is the subject of calibration, a clock generator 3020 to generate a reference clock for the calibration mode, signal generators 3030.1 and 3030.2 generating modulating signals to be used for calibration, a spectrum analyzer 3040 to measure the power of a signal transmitted from adaptive array radio device 3010, a power divider 3060 arranged between signal generators 3030.1, 3030.2 and adaptive array radio device 3010, a circulator 3050 to selectively pass through a signal in a direction from a node corresponding to signal generator 3030.2 of power divider 3060 towards spectrum analyzer 3040 and in a direction from signal generator 3030.2 towards power divider 3060, attenuators 3070.1-3070.n provided between the nodes corresponding to the plurality of antennas of adaptive array radio device 3010 and the plurality of input/output nodes of the power divider, and a control personal computer (referred to as “control PC” hereinafter) 3100 to control the calibration operation.
Power divider 3060 may be a Butler matrix.
A conventional calibration operation will be described briefly hereinafter.
Based on a measurement device control signal from control PC 3100, signal generators 3030.1 and 3030.2 generate modulating signals for calibration. These modulating signals are applied to adaptive array radio device 3010 via power divider 3060 and attenuators 3070.1-3070.n.
At adaptive array radio device 3010, the transmission weight is adjusted so as to have directivity with respect to a signal from signal generator 3030.1 in accordance with the radio device control signal from control PC 3100. If the transmission characteristic of the reception signal path matches the transmission characteristic of the transmission signal path of adaptive array radio device 3010 in this state of affairs, the power of the signal towards signal generator 3030.2, i.e. the power detected by spectrum analyzer 3040, should be “0”.
However, in practice, there is deviation in the transmission characteristic of the reception signal path from the transmission characteristic of the transmission signal path in adaptive array radio device 3010. Therefore, a correction value must be applied to the amplitude and phase of the transmission weight calculated at adaptive array radio device 3010 so as to adjust the power detected at spectrum analyzer 3040 to become “0”.
To this end, the correction values to be applied to the amplitude and phase of the transmission weight calculated at adaptive array radio device 3101 are sequentially modified while monitoring the measurement value of spectrum analyzer 3040 to find an optimum correction value.
By such a procedure, calibration can be conducted with respect to adaptive array radio device 3010.
However, in the conventional calibration system 3000 set forth above, the reception timing of adaptive array radio device 3010 is in synchronization with the signal output timing of signal generators 3030.1 and 3030.2 of the measurement system based on a clock signal from a common clock generator 3020.
If the sampling timing of analog-digital conversion (A/D conversion) carried out during signal processing at adaptive array radio device 3010 is an integral multiple of or is 1/integer times the external clock in such a system, the timing between the measurement system and adaptive array radio device 3010 can be made to match without any error. In practice, the sampling timing of A/D conversion is not an integral multiple of or 1/integer times the external clock. Therefore, there is some error between the timings thereof. Thus, there was a problem that there is an error in the calibration correction value.
It is to be further noted that calibration processing is carried out with the synchronization of the reception signal fixed, based on the assumption that the apparatus is configured so as to establish synchronization between the measurement system and adaptive array radio device 3010. However, even with such measurement form based on fixation, the occasion arises where there is deviation of approximately several symbols in synchronization between adaptive array radio device 3010 and the measurement system due to aging and the like. There was a problem that the clock must be adjusted again on such events.
In view of the foregoing, an object of the present invention is to provide a radio apparatus that can conduct calibration processing of transmission directivity properly for an adaptive array radio device, a calibration system, a calibration method of transmission directivity, and a calibration program of transmission directivity.